I was playing around with the xml parser and wrote a dtd to validate JPatch files.
It can be downloaded here and should be able to validate current (0.5) jpatch models and animations.

When writing the dtd I've found some problems that should be avoided in future versions of JPatch's file format:

The same tags are used in model files and choreographies, but have different meaning there. I don't want to use namespaces as they blow up the document size and there's no namespace support in DTDs either (I know, I could use schema...). But I think it would be better to keep the DTDs separate for model and animation files.

It might make sense to use IDs and IDREFs to reference e.g. attached controlpoints - right now the format uses implied numberings - e.g. all cps are numbered (starting from 0) when the document is parsed.

Don't worry, all future versions of JPatch will be able to load models made with "old" versions. I can't garantee this for animations right now though.